1. Field of the Invention
The present invention relates to silicon carbide semiconductor devices.
2. Description of the Background Art
Conventionally, silicon has been widely used as a material for a semiconductor device. In recent years, silicon carbide has been increasingly employed as a material for a semiconductor device.
Silicon carbide is a wide band gap semiconductor having a band gap wider than that of silicon. By employing the silicon carbide as a material for a semiconductor device, a higher breakdown voltage and loss reduction of the semiconductor device can be achieved, and the semiconductor device can be used in a high-temperature environment.
In order to achieve a higher breakdown voltage of a semiconductor device, studies have been conducted on the structure of a semiconductor device in addition to the material of a semiconductor device. By way of example, a study has been conducted on an outer peripheral structure (also referred to as a termination structure) surrounding the outer periphery of an element region in a silicon carbide semiconductor device. When a high voltage is applied to a silicon carbide semiconductor device, the outer peripheral structure performs the function of relaxing electric field concentration. The relaxed electric field concentration can lead to a higher breakdown voltage of the silicon carbide semiconductor device.
Various proposals on the outer peripheral structure of a silicon carbide semiconductor device have been described in documents. Examples of the documents include Japanese Patent Laying-Open No. 2003-101039, Japanese Patent Laying-Open No. 2008-270412, Hiroyuki Matsunami, Noboru Otani, Tsunenobu Kimoto, and Takashi Nakamura, “Semiconductor SiC Technology and Application,” second edition, Nikkan Kogyo Shimbun, Ltd., Sep. 30, 2011, p. 341 and p. 353, and Hiroki Niwa, Gan Feng. Jun Suda, and Tsunenobu Kimoto. “Breakdown Characteristics of 12-20 kV-class 4H-SiC PiN Diodes with Improved Junction Termination Structures,” Proceedings of the 2012 24th International Symposium on Power Semiconductor Devices and ICs, 3-7 Jun. 2012, Bruges, Belgium, p381-384, and Hiroki Niwa, Jun Suda, and Tsunenobu Kimoto, “21.7 kV 4H-SiC PiN Diode with a Space-Modulated Junction Termination Extension,” The Japan Society of Applied Physics, Applied Physics Express 5 (2012) 64001, 64001-1-64001-3.